1. Field
The disclosure relates to a parking brake for a vehicle. More particularly, the disclosure relates to a parking brake for a ball-in-ramp brake caliper type parking brake for a vehicle.
2. Description of the Related Art
In general, brakes for a vehicle are adapted to decelerate or stop a running vehicle, and include a drum brake and a disk brake. Also, parking brakes for keeping a vehicle stopped during parking of the vehicle generally include a drum type parking brake integrally installed in a drum brake and a disk type parking brake integrally installed in a disk brake. Such a parking brake is connected to a parking cable for operating the parking brake, and the parking cable is connected to a parking lever directly manipulated by a driver or a cable adjusting unit operated by an electric motor unit in such a manner that the parking cable can be operated manually or automatically.
In the case of the disk type parking brake, disk pads are attached on opposite side surfaces of a disk, which is rotated together with a wheel of a vehicle, to generate a braking force.
A general disk type parking brake includes a disk rotated together with a wheel of a vehicle, inner and outer disk pads installed on inner and outer sides of the disk, a caliper housing for operating the inner and outer disk pads, a piston installed in the caliper housing, a carrier movably supporting the caliper housing, and an actuator for actuating the piston.
The caliper housing is slidably installed in the carrier fixed to a knuckle of a body of the vehicle to be located on one side of an outer periphery of the disk. A cylinder is provided in the caliper housing and the piston is reciprocated in the cylinder. The piston moves forward within the cylinder to tightly press the inner disk pad to the disk.
The actuator is connected to a parking cable, and presses the piston toward the disk if the parking cable is operated.
Such actuators include a cam-strut type actuator using a cam rotated by operation of a parking cable and a strut installed between the cam and a piston, and a ball-in-ramp type actuator having a fixed ramp plate fixed to the interior of a caliper housing, a rotary ramp plate rotated by operation of a parking cable connected to a lever member, balls installed between the fixed ramp plate and the rotary ramp plate, and a push rod located adjacent to the rotary ramp plate to push a piston.
Meanwhile, in the ball-in-ramp type actuator, a shaft extending to the outside of the caliper housing is connected to the rotary ramp plate and the lever member is coupled to the shaft to rotate the rotary ramp plate, in which a sealing member is installed at a circumference of the shaft to seal a portion between the caliper housing and the lever member.
However, the sealing member installed at a circumference of the shaft between the caliper housing and the lever member is twisted by the friction between the lever member and the shaft when the lever member and the shaft are rotated during a braking operation, thereby causing a contact portion between the lever member and the shaft to get loose and deteriorating sealing efficiency. Thus, moisture and foreign substances cannot be effectively prevented from penetrating the interior of the caliper housing or the shaft. Accordingly, the parking brake according to the related art causes stains on a shaft portion of the rotary ramp plate due to the penetration of moisture and foreign substances, so that the braking performance is deteriorated.